Organic EL (Electro-Luminescent or electroluminescent) elements are current-driven self-light-emitting elements, and do not need a back light source. Further, the organic EL elements have advantages such as low power consumption, wide viewing angle, and high contrast ratio. Accordingly, organic EL elements are expected in development of applying flat panel display apparatuses.
In an organic EL display device using such an organic EL element, there are provided a number of pixels each formed by using R (Red), G (Green), and B (Blue) sub-pixels. By combining the colors of these sub-pixels, the organic EL display device can display images using a wide variety of colors. These RGB sub-pixels can be arrayed in various types of arrangement. Generally, such sub-pixels are arranged in a stripe arrangement in which sub-pixels of three colors are arranged side by side equally (a so-called RGB vertical stripe arrangement). The display apparatus can display full colors by adjusting luminance among these three color sub-pixels in each pixel. Usually, three neighboring sub-pixels in R, G, and B, are collectively worked as a single pixel (so called as “dot”) having a rectangular shape, and a square arrangement of such pixels realizes a dot matrix display. The dot matrix display apparatus handles image data to be displayed, which forms an n×m pixel data matrix, in one-to-one correspondence with the pixels, so that the display apparatus can display a correct image.
Organic EL display devices can be classified into two types of display apparatus employing a standard of white organic EL elements, i.e., a color-filter type of display apparatus in which three colors of R, G, and B are produced by the color filter, and a side-by-side type of display apparatus in which sub-pixels are separately deposited with organic materials for three colors of R, G, and B. In the color-filter type, since a color filter absorbs a light partially, there are disadvantages that the light utilization efficiency decreases and power consumption increases. On the other hand, in the side-by-side type, a color gamut can be widened easily because of high color purity of the reproduced colors, and the light utilization efficiency increases because of not using the color filter. Accordingly, organic EL display devices of the side-by-side type have come to be used widely.
In the side-by-side type, a FMM (Fine Metal Mask) is used for depositing the sub-pixels separately with organic materials. With request of higher definition of organic EL display devices in recent years, the pitch of the FMM also requests higher precision, which makes a problem that production of the organic EL display devices becomes difficult. In view of the problem, there have been proposed the following pixel array structure utilizing the human being's color vision which is insensitive to colors of R and B and sensitive to G (a so-called PenTile arrangement), as disclosed in, for example, U.S. Pat. No. 6,771,028B, US2002/0186214A, US2004/0113875A, and US2004/0201558A. In the PenTile arrangement, each pixel is composed of sub-pixels in two colors of G and B, or G and R, and a pixel can apparently reproduce a certain color expression which needs a sub-pixel in a missing color in comparison to the RGB arrangement, by using a neighboring pixel including a sub-pixel in the missing color together with the sub-pixels of itself.
In the PenTile arrangement, since sub-pixels are smaller in number than those of the RGB vertical stripe arrangement, the dot width of each of R and B colors can be secured by a length corresponding to the width of two vertical stripes of the RGB vertical stripe arrangement. Accordingly, an aperture size of the FMM can be made larger, which makes the production of high-definition organic EL display devices easier. However, the PenTile arrangement is aimed at softening lack of color reproduction due to the reduction of the number of sub-pixels by using a technique of tiling, and will cause the following defects. For example, jaggies, which are step-wise line, appear in place of a curve lines to be originally displayed smoothly, and a line-shaped color change appears in an image of changing a color gradation and luminance continuously.
From such a circumstance, as a pixel array structure where the size of sub-pixels can be made larger than the conventional RGB vertical stripe arrangement and does not take place the deterioration of display quality similarly to the PenTile arrangement, there have been proposed the following pixel array structure (a so-called S-stripe arrangement) as disclosed in, for example, Japanese Unexamined Patent Application Publications (JP-A) No. 2011-249334 (corresponding to US2011/291550A). In the S-stripe arrangement, R sub-pixels and G sub-pixels are arranged alternately in the same column, and B sub-pixels are arranged in a column next to the column of R and G sub-pixels to as to be arrayed in a raw together with pairs of R and G sub-pixels. In this S-stripe arrangement, the width of sub-pixels can be made wider than those of the RGB vertical stripe arrangement, and an aperture size of the FMM can be made larger. Further, since RGB sub-pixels are all arranged in a single pixel, the S-stripe arrangement can provide an enhanced display quality in comparison to the PenTile arrangement.
Generally, among the RGB colors, the color which is the maximum in relative luminosity is G, followed by R and B in order, and the relative luminosity of G is higher than those of R and B. Therefore, depending on the arrangement of R, G, and B sub-pixels in a pixel, unbalance (deviation) arises in spatial distribution of relative luminosities within the pixel. For example, in the RGB vertical stripe arrangement, a G sub-pixel is arranged at the center of the pixel. Such an arrangement makes the spatial distribution of the total sum of relative luminosities of RGB colors the maximum at the center of gravity of the pixel, and reduces the unbalance of the relative luminosities within the pixel. On the other hand, in the PenTile arrangement, a G sub-pixel is arranged in a column adjacent to an edge of pixel; and in the S-stripe arrangement, a G sub-pixel is arranged at a corner of a pixel. The PenTile and S-stripe arrangements make the maximum position of the spatial distribution of the total sum of relative luminosities of RGB colors separated from the center of the pixel, and the unbalance of the relative luminosities increases within the pixel.
The unbalance of the relative luminosities is hardly perceived at an inner part of a displayed object in an image, but can be perceived conspicuously and causes a phenomenon such that an edge in an image is observed as being colored (so-called “color fringing”) in the case where an image includes an edge extending along the row or column direction of pixels. Particularly, in the S-stripe arrangement, a G sub-pixel is located at the farthest position from the center of gravity of a pixel when being viewed along a diagonal line which does not pass the G sub-pixel among the diagonal lines of the pixel. Such arrangement makes the unbalance of relative luminosities remarkable, and further causes the deterioration of display quality due to the color fringing, which is a large problem. The present invention seeks to solve the problems.